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Excitation 2.jpg


Latin excitāre, frequentative of exciēre to set in motion, awaken, call forth, instigate, < ex- out + ciēre to set in motion.


b : to rouse to an emotional response <scenes to excite the hardest man to pity>
c : to arouse (as a strong emotional response) by appropriate stimuli <excite enthusiasm for the new regime — Arthur Knight>
b : to produce a magnetic field in <excite a dynamo>

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Excitation is an elevation in energy level above an arbitrary baseline energy state. In physics there is a specific technical definition for energy level which is often associated with an atom being excited to an excited state.

In quantum mechanics an excited state of a system (such as an atom, molecule or nucleus) is any quantum state of the system that has a higher energy than the ground state (that is, more energy than the absolute minimum). The temperature of a group of particles is indicative of the level of excitation (with the notable exception of systems that exhibit Negative temperature).

The lifetime of a system in an excited state is usually short: spontaneous or induced emission of a quantum of energy (such as a photon or a phonon) usually occurs shortly after the system is promoted to the excited state, returning the system to a state with lower energy (a less excited state or the ground state). This return to a lower energy level is often loosely described as decay and is the inverse of excitation.

Long-lived excited states are often called metastable. Long-lived nuclear isomers and singlet oxygen are two examples of this.[1]